(1) Field of the Invention
This invention relates to the use of masks using attenuating phase shifting material for regions of the pattern with relatively large spaces between lines and binary mask patterns using opaque material for regions of the pattern with relatively small spaces between lines on the same mask substrate. The mask is illuminated using off axis illumination when using the mask to form a pattern on an integrated circuit wafer. The mask is formed using a single resist layer exposed using multiple electron beam exposure doses.
(2) Description of the Related Art
U.S. Pat. No. 5,481,332 to Shiraishi describes a projection exposure method and apparatus for improved image transfer from photomasks having periodic and non-periodic patterns. The projection optical system uses off axis illumination to illuminate the photomask.
U.S. Pat. No. 5,503,951 to Flanders et al. describes a method of forming a photomask using attenuating phase shifting material.
U.S. Pat. No. 5,480,747 to Vasudev describes a method of forming a photomask using attenuating phase shifting material and using embedded absorbers.
A patent application ( ) entitled xe2x80x9cA NEW DOUBLE LAYER METHOD FOR FABRICATING A RIM TYPE ATTENUATING PHASE SHIFTING MASKxe2x80x9d, Ser. No. 08/956,971, Filed on Oct. 3, 1997, and assigned to the same assignee describes a method of forming multiple patterns in a single layer of resist using two different electron beam exposure doses.
A patent application ( ) entitled xe2x80x9cA MASK AND SIMPLIFIED METHOD OF FORMING A MASK INTEGRATING ATTENUATING PHASE SHIFTING MASK PATTERNS AND BINARY MASK PATTERNS ON THE SAME MASK SUBSTRATExe2x80x9d, Ser. No. 09/020,502, Filed on Feb. 9, 1998, and assigned to the same assignee describes a binary mask pattern and a rim type attenuating phase shifting mask pattern formed on the same transparent mask substrate.
A paper entitled xe2x80x9cOptimization of the optical phase shift in attenuated PSM and application to quarter micron deep-UV lithography for logicsxe2x80x9d by K. Ronse et al., SPIE Vol. 2197, pages 86-98 discusses optical techniques to achieve optimization of attenuated phase shifting masks.
A paper entitled xe2x80x9cQuarter Micron Lithography System with Oblique Illumination and Pupil Filterxe2x80x9d by S. Orii et al., SPIE Vol. 2197, pages 854-868 discusses the usefullness of pupil filtering.
A paper entitled xe2x80x9cDependency of side-lobe effect of half-tone phase shift mask on substrate material and topology, and its solutionsxe2x80x9d by Sung-Chul Lim et al., SPIE Vol. 2512, pages 372-383 discusses loss of resist due to side lobe effect.
In the manufacture of semiconductor integrated circuit wafers photolithographic processing methods having good resolution and a large depth of focus are required to form fine lines. The need for very close spacing between the fine lines places added requirements on the photolithographic processing. In regions of the pattern where the spacing between the fine lines is relatively large the use of masks using attenuating phase shifting material produces good results. In those regions of the pattern where the spacing between the fine lines is small, however, attenuating phase shifting material will not give good results due to side lobe effect.
In regions of the pattern where the spacing between the fine lines is small improved results can be obtained using binary masks and off axis illumination, OAI, of the masks. In the case where the parallel lines are in predominantly one direction dipole illumination using off axis illumination works well. In those cases where the parallel lines are in more than one direction quadrapole illumination using off axis illumination will be required.
It is a principle objective of this invention to provide a method of forming a mask having both attenuating phase shifting patterns and binary patterns on the same mask.
It is another principle objective of this invention to provide a method of exposing a layer of photoresist on a substrate using quadrapole off axis illumination of a mask having both attenuating phase shifting patterns and binary patterns on the same mask.
It is another principle objective of this invention to provide a mask having both attenuating phase shifting patterns and binary patterns on the same mask.
These objectives are achieved by forming a layer of attenuating phase shifting material on a transparent mask substrate. A layer of opaque material is formed on the layer of attenuating phase shifting material. The patterns are then formed in both the layer of opaque material and the layer of attenuating phase shifting material. In that part of the pattern comprising lines and spaces wherein the ratio of the width of the spaces between lines to the line width is large the opaque material is removed from the pattern and the pattern is formed using attenuating phase shifting material. In that part of the pattern comprising lines and spaces wherein the ratio of the width of the spaces between lines to the line width is small the opaque material is left in place and forms a binary pattern. The design data used to form the mask is analyzed to determine the regions of the mask in which the opaque material is removed and which regions of the mask the opaque material is left in place.
The mask is then used in a projection system to form the image of the mask on an integrated circuit wafer having a layer of photoresist formed thereon. The mask is illuminated using off axis illumination, preferably quadrapole off axis illumination, and the light passing through the mask is focussed on the layer of photoresist formed on the integrated circuit wafer.
In one embodiment the mask is formed using a single layer of resist. A layer of attenuating phase shifting material is formed on a transparent mask substrate and a layer of opaque material is formed on the layer of attenuating phase shifting material. A layer of resist is formed on the layer of opaque material. The region of the mask where the ratio of the spacing between the lines to the line width is large is exposed with a first exposure dose and the region of the mask where the ratio of the spacing between the lines is small is exposed with a second exposure dose. The resist is then developed leaving a thinner resist pattern in the region of the mask where the ratio of the spacing between the lines to the line width is large. That part of the opaque material and attenuating phase shifting material not covered by resist is then etched away. The resist is then partially etched away thereby removing resist from the region of the mask where the ratio of the spacing between the lines to the line width is large. The opaque material is then etched away from the region of the mask where the ratio of the spacing between the lines to the line width is large leaving a pattern formed of attenuating phase shifting material only. The remaining resist is then removed and the mask is completed.